The use of electric and optical components in information gathering systems is widespread. For example, electric and optical sensors designed to provide information about environmental parameters form a subset of these devices. The most fundamental sensors are elements which react to mechanical stresses or to temperature variations. Strain gauges employ deformable mechanical structures to generate signals indicating mechanical stresses acting on them. Thermocouples use a junction of two dissimilar metals to measure temperature. Optical materials experiencing changes in optical polarization, phase or transmittance under the influence of stress or temperature variations are used in the optical counterparts of these electric devices.
Increasingly, modern applications require that sensors be deployed in hazardous surroundings. These difficult conditions may be created by corrosive or abrasive agents, wide or frequent temperature variations, large mechanical stresses, high pressures as well as any number of other unfavorable factors. The fields of manufacturing, monitoring, testing are among the many areas where such conditions exist. Clearly, sensors employed under these circumstances have to be afforded additional protection.
Prior art teaches to protect electronic components from acidic, basic or oxidizing environments with organic polymeric encapsulants. For example, in U.S. Pat. No. 5,686,162 Polak et al. teach the use of elastomeric silicones for encapsulating integrated circuits. Other references teach the use of organic-compound-containing encapsulating layers or elastomer casings for the same purpose.
These methods of encapsulating electronic components work well in many applications but become insufficient in very harsh environments. In particular, polymeric encapsulants prove insufficient in mechanically challenging conditions situations.
U.S. Pat. No. 5,278,442 to Prinz et al. describes a system of electronic/mechanical packaging prepared by incremental buildup of layers using the thermal deposition spraying technique. This process in used to layer a complementary material around electric components to provide temporary or permanent thermal and mechanical protection to the embedded circuits or components.
Unfortunately, even this system proves insufficient under very harsh working conditions. Specifically, highly resistant metals, i.e., metals having high melting temperatures, would have to play the role of the complementary material to satisfy the mechanical requirements. In addition, highly efficient thermal protection would have to be incorporated into such a package.
Thus, at the present time there is no known method for embedding electric or optical components in housings suited for deployment in harsh working conditions. This is especially a problem in the field of sensors, since these elements, more than any others, are directly exposed to the harshest conditions.